The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As a means for converting DC to AC, early inverters by the names of thyratron and mercury rectifier have been replaced mostly by thyrister except for heavy-duty high-voltage circuits used in DC electric transmission, for example.
In general, inverters may be classified into a single-phase inverter and a three-phase inverter. The single-phase inverter can supply AC power to a single-phase load. By the way, electrical equipments such as online electric vehicles employ a plurality of loads which should be supplied with the AC power. The installment of a single-phase inverter per each load exacts high cost.
Therefore, to meet the need for selective supply of current to multiple loads, the generally preferred method has been installing switches such as bi-directional semiconductor switch corresponding to the respective loads and controlling the switches on and off to supply current as needed to the appropriate loads, as shown in FIG. 1.
However, the switch is constructed for switching in both directions as enlarged in the circle of FIG. 1 with exemplary four loads requiring the total of twelve semiconductor switch elements for the 3-level inverter. Such increase of the number of semiconductor switch elements results in a load current reduction as well as a higher cost of the 3-level inverter.